Injection mould with a pre-opening jack

ABSTRACT

Injection mold comprising at least two mold sections (2, 3) between which a mold cavity is delimited. One (3) of the mold sections is provided with an ejector (42) for removing the product after injection molding. The other mold section (2) is provided with a gate (5). To enable the solidified sprue to be separated from the molded article, a bush (8) is also present in which the gate (6) likewise extends. This bush (8) is constructed to be movable to a limited extent relative to the mold section (2) in which the other part (5) of the gate is made. As a result the sprue can be pulled away from the article in a guaranteed manner. The movement of the bush (8) is controlled by a jack (16, 17). Consequently, controlled breaking of the sprue is possible and the advantage arises that, by releasing the pressure on the jack (16, 17), no force has to be overcome when the mold is closed.

FIELD OF THE INVENTION

The present invention relates to an injection mould with a pre-openingjack.

BACKGROUND OF THE INVENTION

An injection mould of this type is disclosed in PATENT ABSTRACTS OFJAPAN, Vol. 13, No. 41 (M-791) (3389), 30 Jan. 1989. In this known mouldthe mould sections which are moved relative to one another to break asprue are driven apart by spring force. After these mould sections havemoved a limited distance apart, the actual mould is opened to releasethe product. In order to ensure that the sprue of the product is brokenbefore release starts and to guarantee the sequence of this movement, itis necessary to use relatively heavy springs to guarantee breakage ofthe sprue. Even if relatively heavy springs of this type are used it isstill not always guaranteed that breakage takes place.

This relatively large spring force has to be overcome again when closingthe mould before the start of a new injection cycle. This implies thatany safety measures fitted which serve to stop the closing movement ofthe mould if undesired articles are present between the mould sections,or in the case of other irregularities, must have a minimum responseforce which is equal to the spring pressure to be overcome.

In practice this means that moulds of this type can not be provided witha blocking protection which functions realistically. Consequently it isnecessary to fit complex cover constructions around the mould, themovement of the various sections of the mould being interrupted as soonas such a cover is opened. This is a circuitous and undesirableconstruction with which, moreover, it is not possible to prevent damageoccurring to the product and/or mould during the closing movement if,for example, injection moulding residues are in the wrong place. The useof a cover is merely a safety precaution for operators and does notprotect the mould and/or the products to be injected. The aim of theinvention is to overcome these disadvantages.

SUMMARY OF THE INVENTION

The insight on which the invention is based is not to carry out thebreaking movement of the sprue relative to the product using springforce, which, in turn, has to be overcome when the mould is closed, butwith the aid of jack means. Said jack means, which are operated by meansof a fluid, are pressurised to break the sprue. With this arrangementany desired force can be chosen. The further opening movement of themould takes place only after the sprue has been broken off. The pressureon said jack means can be released when the mould is closed, so thathardly any force has to be overcome in order to place said jack means inthe starting position. If desired, spring means or further jack meanscan be present to move the jack means back into the starting positionthereof after the pressure thereon has been released. In this way it ispossible, using an injection mould according to the invention, duringclosing to measure, in a very sensitive manner, the resistance which hasto be overcome by the closing mechanism. If said resistance exceeds arelatively low value, the closing operation can be stopped immediately.This implies that, if residual product or other components are presentin the closing path of the injection mould, the closing movement can besuspended without damage being caused to any component.

It is pointed out that French Patent 1,553,114 disclosed an injectionmould in which the injection head is arranged so that it is movablebackwards and forwards. The sprue is broken with the aid of airpressure, which is applied between two adjoining mould section. Leakagewill occur as soon as any movement takes place between said two mouldsections, with the consequence that very large amounts of air arerequired to break the sprue, this being associated with highlyundesirable side effects.

In the case of the construction according to said French patentpublication, the product is blown towards the injection nozzle. This,like the movable construction of the injection nozzle, results inincreased susceptibility to malfunction. Moreover, as a consequence ofthe chosen construction there is a risk that when the mould sections aremoved apart one of said sections will skew and become trapped in theother.

A construction according to the invention can be used in the case of aninjection mould in which the mould cavity is delimited by two mouldsections. It is obviously possible to construct the mould cavity fromthree or more mould sections. This is frequently desirable, especiallyon the grounds of process engineering considerations. In this way it ispossible to produce highly complex articles and to control the injectionand solidification of the plastic composition.

According to an advantageous embodiment of the injection mould describedabove, main operating means are present to move that mould section whichis opposite the mould section comprising the gates relative to saidsection. This is generally known in the prior art, but thesepublications propose the use of auxiliary operating means to move themould section comprising the gate relative to a fixed injection head.

The movement of the various mould sections can be optimised byinstalling auxiliary operating means. This leads on the one hand to thepossibility of obtaining a larger opening for ejection of the productand, on the other hand, to the possibility of shortening the time cycle,because the mould sections can be closed more efficiently.

Although the invention can be used in conjunction with all injectionmoulds according to the prior art, it is used in particular inconjunction with a so-called quick-change mould. When producingrelatively short runs, the time taken to change to the mould for anotherproduct to a large extent determines the price of the products finallyobtained. The aim is therefore to carry out mould changes as rapidly aspossible. In the prior art the change-over time has fallen in recentyears from 5 to 6 hours to 2 hours.

The aim of the present invention is to provide a quick-change mould withwhich change-over can be carried out even more rapidly.

This is achieved by means of an injection mould, as described above,comprising a mother mould in which an auxiliary mould is interchangeablyincorporated, which auxiliary mould comprises at least two mouldsections delimiting the mould cavity, which mould sections can each befixed to the mother mould, one mould section being provided with a bushwhich is movable to a limited extent with respect to said section andcan be connected to the mother mould, whilst the other mould section isprovided with ejector means, the mother mould being provided with aninjection nozzle and means for moving the bush relative to the mouldsection. With this arrangement only the at least two mould sections, thebush and the ejector means are replaced at the time of change-over.

For the quick-change mould described above, accurate centring isrequired only in respect of the section where gating takes place. Theopposite sections of the mould can be fitted with some tolerance.Consequently rapid change-over can be achieved without too manycomplicated fixings.

The invention also relates to a method for injection-moulding anarticle, comprising the closing of mould sections which delimit a mouldcavity, the introduction of plastic into said mould cavity via a gate,removal of the sprue by moving a part of the gate that is some distanceaway from the mould cavity, opening of the mould cavity and removal ofthe article, which method is characterised in that the movement of thatpart of the gate is carried out using a fluid which can be pressurised,and in that no pressure is exerted by said fluid when the mould isclosed for injection.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be explained in more detail below with reference toan illustrative embodiment shown in the drawing. In the drawing:

FIG. 1 shows a mother mould with an auxiliary mould incorporatedtherein, in partial cross-section in the position for introduction ofplastic;

FIG. 2 shows the installation according to FIG. 1 during the first stepof pulling the sprue away from the product;

FIG. 3 shows the installation according to FIG. 2 during the second stepof pulling out the sprue;

FIG. 4 shows the installation according to FIG. 3 during the third stepof detaching and removing the sprue; and

FIG. 5 shows the installation according to FIG. 1 during the step ofejecting the article.

DETAILED DESCRIPTION OF THE INVENTION

The injection mould according to the invention is indicated in itsentirety by 1. In said mould the mould cavity is delimited by the rightmould plate 2, the centre mould plate 3 and the left mould plate 4.Internally the mould cavity is delimited by core 7, which has free end46, and an ejector 42. Said mould cavity is indicated by 18. A part ofthe gate which is indicated by 5 is located in right plate 2. A furtherpart of the gate is located in bush 8 and this part is indicated by 6.Part 6 of the gate opens into a widening 19. Bush 8 is fixed to mouldsection 2 by means of bolts 53. Said bolts 53 are incorporated withtheir heads in chambers in the bush 8 with a play such that bush 8 andmould section 2 can be moved relative to one another over a shortdistance. Bush 8 is provided along part of its circumference with agroove 20 which, when bush 8 is fitted in connecting plate 15, coincideswith a groove 21 in said plate 15, as a result of which a circularopening is delimited in which a dowel pin 10 or the like is fitted inorder to connect bush 8 firmly to plate 15. Connecting plate 15 isprovided with a stepped opening 22, in which a bolt 23 can be fittedwhich can be fixed to a mounting plate 14. Because the length of theshaft of bolt 23 is greater than the thickness of connecting plate 15located underneath it, mounting plate 14 can execute a limited strokerelative to connecting plate 15. Mounting plate 14 is provided withfixings 11 for firmly incorporating right mould plate 2. Connectingplate 15 is provided with a piston chamber 17, in which a piston 16 isfitted so that it can move backwards and forwards. Piton chamber 17 isconnected via a pipe 24 to a plunger unit 25, the casing 26 of which isfirmly connected to the mounting plate 14, whilst the rod 28 connectedto piston 27 can engage on plate 29, which is firmly connected to themachine frame 9. Injection head 30, which, if appropriate, is providedwith a shut-of valve in a manner not shown in more detail and isconnected to a source of fluid plastic material, is fitted in plate 29.Rod-shaped drawing elements 31 are located in the vicinity of injectionhead 30 and the free ends of said drawing elements are provided with atapered section 32, which, as can be seen from FIGS. 1 and 2, can beaccommodated in the cavity produced by the widening 19 in bush 8. Plate48, which is provided with openings for accommodating drawing elements31 and is movable to a limited extend relative to plate 29, is locatedbetween connecting plate 15 and plate 29. Said movement is effected byhook element 49. Said locking device 49 is fixed by means of pin 50 toplate 48 and accommodated by stop 51 such that it can be moved to alimited extent relative to plate 29. Locking device 49 is moved by(slidable) connection with mounting plate 14. Mounting plate 14 isguided, in a manner not shown in more detail, relative to plate 29 sothat the latter is able to move in a controlled manner backwards andforwards relative to plate 29, under the influence of the plunger unit25. To this end, the side lying behind piston 27 is not only providedwith the connection for pipe 24 which has been described above but isalso connected via pipe 33 to a control device 34. The section lying infront of piston 27 is connected via a pipe 35 to control device 34. Onthe other side, the control device 34 is provided with pipes 36, 38leading to a jack unit 39, 40, the housing 39 of which is connected tothe machine frame 9, whilst the piston rod 40 is connected to plate 41,which forms part of the other half of the mould. An ejector 42 is fittedin plate 41, which ejector engages via a yoke mechanism 43 on an ejectorjack 44, which is connected to the frame 9. Pipes 45 and 52 areconnected to said ejector jack. A feed and discharge system, which isnot shown in more detail, for coolant or heating fluid can be located oncore 7 to enable the temperature of the free end 46 to be controlledduring the injection moulding operation. A filler element 47 is attachedto plate 41 and, in turn, is provided with fixing 12 for interchangeablefixing of plates 3 and 4 which delimit the mould cavity.

The installation described above functions as follows. Starting from theposition shown in FIG. 1, both the mould cavity and the gate are filledwith fluid moulding material, such as plastic or an alloy. The course ofsolidification can be controlled by regulating the supply of fluidthrough core 7. Moreover, separate channels for the supply of fluid canbe present in the various mould plates 2-4 delimiting the mould cavity.The connection between the cooling channels of the mould plates and, forexample, filler element 47 can be provided by means of channels whichare centred relative to one another and are sealed with the aid ofO-rings. In this way it is possible in a simple manner to obtain a sealof the cooling channels directly when, for example, mould section 4 ischanged, and it is not necessary to fit separate hoses and the like onsuch a mould section. After the product has solidified sufficiently,starting from the position in FIG. 1, a pressurized fluid, such ascompressed air, is supplied, with the aid of control device 34, via pipe33 to the left side to piston 27 and via pipe 24 to piston 16. Whenpressure is applied to both piston 16 and piston 27 there will initiallybe no effect because the mould is held in the closed position by jacksystem 39, 40. When rod 40 is retracted, filler element 47 moves to theleft and, by appropriate selection of the ratio of the diameter ofpiston 16 relative to that of piston 27, piston 16 will first move fromthe position shown in FIG. 1 towards the left and thus move mountingplate 14 and connecting plate 15 a short distance apart. As a result thebush 8 attached to connecting plate 15 will move slightly relative toright mould plate 2. That is to say, the gate 5, 6 will be lengthenedsomewhat. As a result of the tapering of gate 6 into bush 8 and of thewidening 19, the sprue will always break in a controlled manner at thepoint of attachment to the product when a tensile force is exerted onbush 8. The maximum force for detaching the sprue from the article andremoval from the gate is overcome with the aid of piston 16 (FIG. 2).When rod 40 is further retracted a point is reached at which plates 14and 15 can no longer be driven further apart because they are stopped bybolt 23, after which piston 27 is driven to the right, that is to sayhousing 26 together with mounting plate 14 are moved to the left.Because of the presence of the tapered sections 32 of drawing elements31, the sprue is pulled in the manner known from the prior art from gate6 and widening 19 of bush 8 (FIG. 3). When plate 14 is moved further tothe left, plate 48 is pulled to the left, relative to plate 29, by hookelement 49. During this movement the drawing elements come to lieentirely inside plate 48, so that the sprue is detached as shown in FIG.4. When housing 26 is moved to the left, from FIG. 2 to FIG. 3, the leftsection of the mould also moves to the left. That is to say, jack unit39, 40 does not impede the movement when rod 40 is further retracted. Asa result, a relatively large passage is provided for the product to beejected, yet the total opening path is limited, which results in asaving in time. At the end of the retracting movement of rod 40, ejector42 is actuated with the aid of ejector jack 44, as a result of which theproduct falls out of the mould cavity as shown in FIG. 5. In this way itis always guaranteed that the sprue always drops out of the mould in thesame way in a controlled manner.

When plates 14 and 29 are moved towards one another again, piston 16 islikewise moved back into the initial position and plate 48 is movedtowards plate 29 again, so that the tapered ends 32 of the drawingelements 31 are again located in the widening 19. Operated by jack unit39, 40, the left sections of the mould are then moved to the right againand the mould is closed, so that a fresh injection moulding operationcan take place. In this way it is not necessary when the mould is closedat a later stage to overcome the force for moving piston 16 back intothe starting position, because said piston has already been moved back.Partly as a consequence of this, it is possible to provide a so-called"soft close". This is understood to mean that the jack unit 39, 40 isoperated using a relatively low pressure, so that the movement isstopped immediately if there is any hindrance whatsoever in the movementpath of the left sections of the mould. Moreover, this movement underlow pressure can take place at a relatively high speed under effectivecontrol.

For changing the mould in order to produce a different product it isnecessary only to detach fixings 10, 11 and 12. By this means the mouldplates 2, 3 and 4, together with bush 8, will be detached, possiblyaccompanied by the ejector mechanism 42. The latter depends on the shapeof the following product to be produced. In some cases a number ofejector pins are be used in place of a bush-shaped ejector. Ifappropriate, inlets and outlets for a coolant fluid can be presentbetween the various mould plates 2, 3 and 4 an the plates 47 and 14respectively. Said inlets and outlets can be connected by means ofinternal channels to fixed parts of the installation in the mannerdescribed above. Controlled solidification can be achieved by coolingthe product in various ways with the aid of sleeve 45 and the outerwalls of the product with the aid of cooling in the mould plates 2-4. Itis clean that this type of replacement of the mould sections can becarried out particularly rapidly. As an example, a change-over time of2-5 minutes may be mentioned, compared with the change-over time of 2hours which is customary according to the prior art.

Decentralised and centralised injection of products can be achieved in aparticularly simple manner using the above construction. A particularlyhigh stability can be achieved because the fixed parts of the so-calledmother mould can be of heavy construction. The course of the process canbe accurately controlled by means of further cooling, which is notshown. Centring of the various plates 2-4 relative to the adjacent partscan be carried out in any manner disclosed in the prior art. Onepossibility is to provide thickenings which fit in correspondingcavities. With the installation according to the invention, changing ofthe mould plates 2, 3 and 4 together with bush 8 is so simple that thiscan be carried out with the aid of a robot, so that fully continuousoperation without a significant number of operators is possible.

Although the invention has been described above with reference to apreferred embodiment, it must be understood that numerous modificationscan be made thereto. Thus, it is possible to use the mechanism forremoval of the sprue with other types of moulds which are known in theprior art. Said moulds can also be injection moulds for very large runswhich do not have the constructional features for rapid changing as inthe case of the present invention. All such modifications fall withinthe scope of the present Application.

We claim:
 1. In an injection mould comprising a stationary injectionhead (30) and at least two mould sections which delimit a mould cavityand are movable relative to one another, a gate (5) being fitted in onemould section (2) and a movable bush (8) being fitted adjoining saidmould section (2) remote from the other said mould section (3), throughwhich bush (8) the gate also extends, means being present to move thebush (8) relative to said mould section (2), as well as stop means tolimit said movement; the improvement wherein said means for moving thebush (8) relative to said mould section (2) comprises a mounting plate(14) to which said one mould section (2) is adapted to be fixed, aconnecting plate (15) which is movable to a limited extent relative tosaid mounting plate (15) and to which the bush (8) is adapted to befixed, and jack means which operate between said plates (14, 15). 2.Injection mould according to claim 1, wherein jack means (39, 40) arepresent to move said mould section (4), remote from said mould section(2) comprising the gate, relative to the last-named mould section (2)and wherein auxiliary jack means (25) are present to move saidlast-named mould section (2), which comprises the gate, relative to afixed injection head (30).
 3. Injection mould according to claim 1,wherein means for removing sprue engage close to the side of the bushfacing away from mould section (2).
 4. Injection mould according toclaim 1, comprising a mother mould in which an auxiliary mould isinterchangeably incorporated, which auxiliary mould comprises at leasttwo mould sections (2, 4) delimiting the mould cavity, which mouldsections must each be fixed to the mother mould, one mould section (2)being provided with the bush (8) which is movable to a limited extentwith respect to said one mould section and must be connected to themother mould, whilst the other mould section (4) is provided withejector means, and wherein the mother mould is provided with aninjection nozzle (30).